Estrogens are implicated in the development of ovarian cancer and estrogen receptors (ER) alpha and beta are present in 20-100% of ovarian cancer patients. For this reason, antihormonal therapy with anti-estrogens or ER-antagonists is potentially an attractive treatment option. However, only a small proportion of patients (5-19%) will respond to antihormonal therapy. ER-expression in ER-positive breast cancer can be assessed by positron emission tomography (PET) with [18F]fluoroestradiol (FES). In this study the investigators will evaluate whether FES-PET can be used to visualize and quantify ER-expression in ovarian cancer. If these results are positive, this would warrant further exploration of FES-PET imaging in ovarian cancer.

Investigators will evaluate whether FES-PET can be used to visualize and quantify ER-expression in ovarian cancer. If these results are positive, this would warrant further exploration of FES-PET imaging in ovarian cancer.

Inclusion Criteria:

1. Histological evidence or high clinical suspicion of epithelial ovarian cancer
2. The presence of at least one measurable lesion (RECIST version 1.1).
3. Histology or cytology can be obtained (may be ascites)
4. Eastern Cooperative Oncology Group performance status 0-2.
5. Postmenopausal status (defined as either >45 years with amenorrhea >12 months, or prior bilateral ovariectomy)
6. No history of other ER-positive malignancies
7. Signed written informed consent
8. Able to comply with the protocol

Exclusion Criteria:

1. Use of estrogen receptor ligands, including tamoxifen, fulvestrant or estrogens, during the 5 weeks before entry into the study
2. Life-expectancy ≤ 3 months